The overall aim of this project is to address a key rate-limiting step in the development of therapy for Duchenne Muscular Dystrophy: systemic gene delivery. We focus on a direct gene transfer approach to this problem and specifically avoid any dependence on chronic immunosuppression. We build on compelling proof-of-concept studies from multiple labs using similar adeno-associated virus (AAV) vectors in dystrophic mice and our previous discovery that forced extravasation of vector during retrograde infusion can be used as a means to efficiently transduce both skeletal and cardiac muscle in non- dystrophic large animals. We hypothesize that the underlying mechanism of vector transport relies on pressure-induced, reversible alteration in the scale-dependent barrier function of the venular endothelium. We demonstrate that this hypothetical mechanism is consistent with the observed highly efficient global pattern of gene transfer to muscle during systemic, retrograde infusion in the setting of profound hypothermia and balloon occlusion of the great vessels. The experiments proposed address several additional hypotheses that should lead the way to safe and efficient gene transfer directly to all muscles in the canine model for Duchenne muscular dystrophy. We will concurrently test several hypotheses about serial measures of locomotive, respiratory and cardiac muscle function in the dog and then apply the new knowledge in the study of pups randomized to undergo gene transfer at varying doses. Successful completion of the experimental plan will provide general information relevant to the biological response to somatic gene delivery and the preservation of organ function during profound but rapidly reversible alterations in endothelial integrity. It will also provide specific information about the rational design of strategies for systemic gene therapy in one of the most common single-gene lethal diseases in man, Duchenne Muscular Dystrophy.